1. Field of the Invention
The present invention relates to an image processing apparatus, and its control method and control device. In particular, the present invention relates to an image processing apparatus which employs a combination of primary and secondary storages wherein given image data is stored in the secondary storage through the primary storage, and to its control method and control device. More specifically, the present invention relates to an image processing apparatus such as a digital copier, a facsimile apparatus, a printer, and so forth wherein image data finally stored in the secondary storage is output in a desired timing in a desired manner.
2. The Description of the Related Art
Digitization on image processing apparatus, such as a copier, progresses in recent years, and, also, for the purpose of image data processing and editing, a semiconductor memory (image memory) is utilized in many cases. An image processing apparatus such as a digital copier has a copy function including a so-called “electronic sorting” function. This function is such that a plurality of sheets of paper to be copied are first stored in a semiconductor memory collectively, and, then, the thus-stored image data is printed out in a manner such that each of the sheets of paper is copied, one by one, in a desired manner. By this function, a sheet classification work after the copy can be reduced remarkably.
In such a machine, it is necessary to hold temporarily image data of a plurality of pages. In this case, if such a large amount of image data is stored in a semiconductor memory (primary storage), as the semiconductor memory has a not so reduced unit price per storage capacity, the machine itself may become increased in the total price. For solution of this problem, a mass storage device such as a hard disk drive having a relatively reduced unit price per storage capacity is employed in addition to the semiconductor memory.
In such a case, image data input through a scanning device or the like is first stored in a semiconductor memory, and, then, if needed, the same image data is transferred to the above-mentioned mass storage device in which the image data is then held.
In order to perform input and output (reading and writing) of image data to/from the image memory which consists of the above-mentioned semiconductor memory, a direct memory access controller (referred to as a DMAC, hereinafter) may be used in many cases.
DMAC performs control for outputting and inputting image data from/to a memory area of the image memory based on memory area management information called a ‘descriptor’. In this case, a plurality of descriptors are provided, and the whole memory area is divided into the respective division areas, each of which is controlled by the respective one of the descriptors.
Thus, it becomes possible to perform input and output of image data to/from an image memory having a storage capacity smaller than the whole data amount of the image data, by using the image memory divided into a plurality of memory areas used in a form of, for example, a ring buffer.
In memory control using DMAC, it is possible to perform, individually for respective descriptors, control of progress (starting/terminating) of input and output (transfer) of image data on data amount specified for each descriptor, and execution timing control (control of interrupting/resuming of input and output of image data in predetermined timing) of transfer of the image data in amount specified for each descriptor. For this reason, according to memory control using DMAC, flexibility of timing control of input and output of image data to/from a semiconductor memory and another mass storage device controlled under DMAC is high, and, thus, it is possible to apply this control scheme to a wide range of memory application field.
In general, a plurality of sets of image data cannot be simultaneously input/output (written into/read out) to/from the above-mentioned mass storage device such as a hard disk drive (HDD). However, by utilizing such a memory control scheme using DMAC, data transfer job to the above-mentioned mass storage device can be divided into a plurality of ones by the respective descriptors, and thereby, it is possible to process each data transfer job in a time division manner. Thereby, the image data divided into the plurality of sets can be transferred in parallel apparently.
However, when using processing in time division manner, the time which data transfer takes as total does not become shorter. For this reason, in case improvement in productivity of apparatus is strongly requested, i.e., a digital copier, or the like, such a method of applying time division manner cannot necessarily be said to be an optimum method. In order to solve this problem, once image data is compressed, and, after that, it is transferred into the storage device. Thereby, it is possible to substantially reduce the amount of data to be transferred and written to the storage device. As a result, it is possible to effectively reduce the time required, and, thus, to improve the productivity or yield of the system/apparatus such as a digital copier.
Furthermore, for the purpose of simplification of memory control, a scheme may be applied, in which, rather without applying the time division manner, but a mass storage device is occupied for a predetermined time interval, and, during the interval, in synchronization with image inputting operation by a scanner or the like, transfer of the same image data to the mass storage device is performed.